Sericostoma bergeri Malicky 1973

Waringer, Johann & Malicky, Hans, 2017, The larvae of Sericostomabergeri Malicky, 1973 and Sericostomaherakles Malicky, 1999 (Trichoptera, Sericostomatidae), ZooKeys 695, pp. 123-133 : 124-125

Sericostoma bergeri Malicky 1973

Description of the 5th instar larva.

Diagnosis. Pronotum with convex ventral border; anterolateral pronotal corner short and knob-like; with black comma-like marking on lateral protuberance; setal counts on abdominal dorsum IX 18-41.

Biometry. Body length of 5th instar larvae ranging from 16.0 to 17.5 mm, head width from 1.69 to 1.76 mm (n = 3).

Head. Head capsule roundish, dorsally medium to orange brown, posterolaterally and ventrally whitish; with slightly granulated surface and large, elongated, orange muscle attachment spots (Figs 1-3). Distinct whitish spade-like patch present around each eye (Fig. 3). With ridge extending from posterodorsal corner of white spade-like ring around each eye (Fig. 3) to anterior parietal margin where ridge creates an inwardly-bending groove bearing the antenna (Fig. 1, arrow). Frontoclypeus with shallow central constriction; a shallow secondary constriction situated subapically near anterior border (Fig. 1). Head capsule with complete set of 18 pairs of primary setae: 10 dorsal and 2 ventral primary setae on each parietal, 6 pairs of primary setae on frontoclypeus. Labrum medium brown, narrowly rectangular, with 6 pairs of primary setae. Submentum separating the genae incompletely, broadly shield-shaped, light brown, with darker brown rectangular anterior sclerotization (Fig. 2). Mandibles blackish brown, of shredder type, with 4 terminal teeth (Fig. 2).

Thorax. Pronotum dark brown (Fig. 5), in some specimens slightly paler on posterior half (Fig. 3). Without transverse ridge present in other caddisfly taxa (e.g., Limnephilinae), heavily sclerotized, with anterolateral corner creating a tiny, knob-like projection (Fig. 4, white circle). The two pronotal plates mesially meeting in a narrow, straight suture; surface smooth (Fig. 5). Ventral pronotal margin curved (Fig. 4, dotted line). Each pronotal half covered by 223-235 setae concentrated on anterior pronotal section. Anterior pronotal margin with row of pale, curved setae (Fig. 3). Anterior process of propleuron long and corniform (Fig. 7, arrow). Mesodorsum covered by 4 sclerotized plates (2 large central, 2 small lateral), anterior border medium brown, with oval, pale muscle attachment spots, posterior section whitish, with brown muscle attachment spots (Fig. 5); suture between central and lateral plates inconspicuous (Fig. 6, arrows). Setal counts per central sclerite are 64-72 in anterior group and 25-30 in posterior group; lateral sclerite with 49-57 dark setae (Fig. 6).

Prosternal sclerites and prosternal horn lacking. Metadorsum covered by colourless and barely visible weak sclerites arranged in 2 parallel transverse bands. Setal counts per sclerite are 27-35 setae in anterior group, 40-46 setae in posterior group (Fig. 5).

Legs medium to light brown (Figs 7-9). Foreleg short and stout, femur distally enlarged and flattened, thereby creating an edge interacting with tibia when bent inwards (Fig. 7). Coxa with ventral group of long black setae, trochanter with dense ventral brush of pale, flexible setae. Dorsal edge of femur with large groups of dark setae. Tibia with groups of long dark dorsal and ventral setae and with pale apical spine. Strong tarsal claw sickle-shaped, with stout pale basal spine. Midleg much more slender, coxa weakly sclerotized, femur not enlarged. Hind leg even more slender, tarsal claw elongated, setation less than in other legs (Figs 7-9).

Abdomen. Abdominal segment I with 2 flat, oblique lateral and 1 low, inconspicuous dorsal protuberances (Fig. 10); setation consisting of 1 pair of ventral sa1 setae (Fig. 11, arrows) and 1 lateral protuberance seta per side (Fig. 11 lp). With black comma-like marking on lateral protuberance (Fig. 10, arrow). Gills consisting of tiny single (rarely double or triple) filaments and in presegmental position only. Dorsal gills present at most from abdominal segment I to VI, ventral gills from segment II to VII and lateral gills from II to III. Lateral fringe lacking; however, with lateral rows of tiny serrate lamellae on each side of abdominal segments III to VII (Fig. 12), and with row of forked lamellae on each side of segment VIII (Fig. 13).

Dorsal sclerite of abdominal segment IX lacking, soft cuticle with 18-41 black setae of almost equal length on posterodorsal border (Figs 14, 15pds). Dorsum of each anal proleg with cluster of 35-45 black setae (Figs 14, 15 aps). Lateral sclerite of anal proleg with 28-35 black setae of varying length (Fig. 14 ls). Anal proleg claw with sharply angled crook and dorsal accessory hook (Fig. 14, arrow).

Larval case. Cylindrical, tapering, curved, made of flat sandgrains of approximately uniform size, neatly arranged in a puzzle-like pattern, thereby creating a rather smooth surface (Fig. 16). Case length 15.7 to 17.6 mm, anterior width 3.3 to 4.1 mm, posterior width 2.6 to 2.8 mm (n= 3). Foramen posterior partly closed by a slightly conical, translucent silken membrane with round central hole 0.61 mm in diameter (Fig. 17).